An optical fiber is a glass or plastic fiber designed to transport a light signal along its length. The use of optical fibers in communication systems permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communications. Signals in optical fibers generally are undisturbed by electromagnetic interference and can be transported with less loss than signals transported via metallic conductors. Light signals are maintained in the core of the optical fiber by total internal reflection which results in the fiber acting as a waveguide. In general, an optical fiber has a core and a cladding typically with the majority of the light in the fiber being confined to the optical core, i.e., the waveguide.
Under certain conditions of power and sufficiently narrow signal spectrum, acoustic waves can be generated in the fiber which interfere with transmission of the optical signal by scattering it. This scattering is known as Stimulated Brillouin Scattering (SBS) and can limit the power transmitted through a fiber or generated in a fiber if it is laser-active. Generally, such interference is limited to high-coherence light sources, i.e., typically those having spectral linewidths less than 100 MHz.
Due to the power limiting effects of SBS, it is generally desirable to suppress it as much as possible. In some cases, suppression has been effected by manipulating the acoustic waveguide properties of the fiber so as to minimize the interaction between optical signals and acoustic waves in the fiber. Since the optical fiber acts both as an acoustic waveguide and as an optical waveguide, it can generally be designed to suppress acoustic transport characteristics, i.e., reduce Stimulated Brillouin Scattering, while maintaining optical transport characteristics. In particular, the optical fiber can be designed (1) so as to increase acoustic waveguide transmission losses (i.e. waveguide attenuation), (2) such that the field distributions in the fiber for the optical and acoustic waves overlap as little as possible, which condition can be effected by manipulating physical boundaries of one or more layers of glass in a fiber, and (3) so as to result in the fiber having many weaker acoustic modes rather than a single very strong acoustic mode. Each of these methods can be utilized independently or in cooperation to suppress SBS.